Analog telecommunications networks are distinguished in that, inter alia, the charge for a communications connection is calculated according to time-unit intervals. Such charge invoicing is also necessary today in the age of digital communications networks, when analog terminals, such as pay telephones, are used as a calling, terminal device.
In order to be able to determine the price of a communications connection according to time-unit intervals, a switching network node connected to the calling terminal device generates time pulses. The switching network node may transmit the generated pulses to the calling terminal device for the purpose of calculating payment, when it is, e.g. a pay telephone. Each pulse corresponds to a specific monetary value. In each instance, the connection price payable per unit time may be set by selecting the interval of consecutive pulses. The conditions for correctly calculating payment according to time-unit intervals are that    a) the difference between the length of the contractually agreed-upon, time-unit interval and the length of the billed time-unit interval does not exceed a predetermined value, which is, as a rule, less than one second;    b) the first pulse is generated in the network node within a predetermined time span after the start of the communications connection; and    c) not more than y time pulses are generated after the end of the communications connection, the last time pulse only being allowed to be generated within a predetermined time span.
Until now, it is believed that there has been no testing methods and testing systems, by which the calculation of a connection price according to time-unit intervals may be validated.
Therefore, the present invention concerns the matter of providing a method and a testing device for verifying the charge invoicing for a communications connection according to time-unit intervals.